The invention relates to maintaining adhesion under conditions of high humidity.
A variety of applications require the maintenance of a structural or semi-structural adhesive bond to glass or between two substrates, one of which is glass, under conditions of heat and high humidity. In the automotive industry, for example, structural adhesives are used to bond metal buttons to glass windshields to provide a base for mounting rear view mirrors. It is difficult, however, to form adhesive bonds that have the long term durability required for particular applications. Adhesive bonds to glass tend to fail over time or when subjected to more rigorous conditions such as heat and high humidity. The interface between the substrate and the adhesive is a particularly weak point in terms of stability in the presence of humidity. Consequently, the more common failure mode is adhesive rather than cohesive.
To improve adhesion, substrates are often treated either chemically, e.g., with a chemical primer, or mechanically, e.g., by abrading the surface. Chemical priming methods involve pre-treating the surface with organic solvents and reactive chemicals such as chromic sulfuric acid, which present environmental and toxicity issues. Mechanical treatments add additional process steps to a manufacturing operation.